Scientists have found a way to safely store notoriously dangerous white phosphorus on the atomic scale: in a cage made of atoms that can only be unlocked by a specific molecule, according to a study published in the journal Science.Containing white phosphorus, a tetrahedral formation of phosphorus atoms, will be useful because the molecule readily reacts if it comes into contact with air.

It’s not surprising, then, that it is often used in military campaigns to create smokescreens to mask movement from the enemy, as well as an incendiary in bombs, artillery and mortars [ScienceDaily]. White phosphorus is also an essential ingredient in many plant fertilizers and weed killers, so the ability to safely transport and store the molecule would also be an asset for those industries.

The phosphorus and the cage, which self-assembles in water, have the same shape: They are pyramids. That means the two structures fit together close to flawlessly. The phosphorous is stabilised because when it usually reacts with oxygen it gains volume. ‘But there is not enough space inside the cage for it to oxidise so it is constricted within the space of the cage,’ says [lead author Jonathan] Nitschke [Chemistry World]. The crystalline cage consists of sulphur, nitrogen, carbon, iron (II) and oxygen, and the molecule key that releases the phosphorus is benzene, an organic compound. The benzene molecule fits inside the cage even better than the phosphorus molecule, and therefore pushes it out.

The molecular cage could offer a solution to combat contamination with white phosphorus, which is known for the way it can “inflict grievous harm” and “poses a major environmental hazard”…. “It is foreseeable that our technique might be used to clean up a white phosphorous spill, either as part of an industrial accident or in a war zone,” said Nitschke [AFP]. Scientists hope to apply the technique to store other dangerous chemicals.